1. Field of the Invention
The invention relates to a circuit arrangement for protected data transmission, particularly in ring-shaped bus systems.
2. Description of Relevant Art
In machine and plant construction today, movements and processes are not infrequently controlled which represent a danger to the life and health of persons, particularly the operating personnel, in the case of a fault or if they fail. Apart from these dangers, however, valuable machine parts must also be protected which can suffer great financial damage in the case of possible malfunctions.
Any faults which may occur must, therefore, be recognized by the process or the existing control facilities and the machine should always be driven in a state which can be considered safe. As a rule, redundant structures are necessary for this which monitor the safety functions independently of the actual control. In machine or plant construction, detection of a single error is frequently sufficient for fault detection. After this fault has been detected, the control process can then be interrupted and stay in a safe state. This prevents any damage by faulty continuation of the process.
The methods for fault detection and the measures necessary for these are stated in international standards DIN V VDE 0801 and DIN ISO 61508. By means of the principles given in these standards, the manufacturers of automation equipment have developed in recent years different strategies which allow safe transmissions on bus systems, see, for example, the “profibus with F-Profil, PNO and safety-bus P by Pilz and Sick.
In addition, control systems will reach the market which already have internally redundant structures and thus, in interplay with said safe-bus systems, allow fault detection; see, for example, the bus systems from Siemens, particularly the equipment series S 7 400 F, or the PSS 3000 series by Pilz.
However, the methods implemented there can only be used with completely new installation of the necessary components and protect only inadequately against systematic faults.